1. Field
This disclosure relates generally to circuits that generate a delta phi signal, and more specifically, to delta phi generator having a start-up circuit.
2. Related Art
Bandgap references typically use a circuit that includes a pair of semiconductor devices, biased at different current densities, to generate a voltage across a resistor that is representative of absolute temperature. When the signals are generated using a pair of bipolar transistors this voltage is called a delta Vbe signal. The semiconductor devices can also be PN junction diodes or MOS transistors. Because the voltage can be generated from devices other than those with a Vbe, a more general term that can be used for this signal is a delta phi signal. The delta phi signal or a signal that is generated coincident with the delta phi signal is then used as a key element in generating a voltage reference or some other useful function. One issue with typical delta phi generators is that there may be two stable states and only one of which is useful in generating the delta phi signal. To overcome this a start-up circuit is provided to ensure that the delta phi generator will be in the desired stable state. One of the difficulties with such start-up circuits is in reliably detecting which state the delta phi generator is in especially while using minimal current to perform the detection. Also due to power glitches, the delta phi generator can switch out of the useful state.
Accordingly there is a need to improve upon the techniques for ensuring that the delta phi generator is in the desired state.